The present invention relates to an internal combustion engine and more particularly, to an air-fuel mixture intake system having two independent intake passages for light and heavy load operations for use in an internal combustion engine.
Conventionally, in an internal combustion engine which is equipped with the so-called dual or duplex air-fuel mixture intake system having two intake passages with respect to a combustion chamber of the engine for light load or low speed operation and heavy load or high speed operation respectively, for example, one disclosed in Japanese Utility Model publication Jitsukosho 31921/76, the intake passage for the light load operation having a small cross sectional area is arranged to be joined, in the vicinity of an intake valve of the engine, into the intake passage for the heavy load operation having a large cross sectional area so that during an idle operation and ordinary low or medium speed operation of the engine, only the light load side intake passage of the small cross sectional area is used for accelerating flow rate of the air-fuel mixture so as to expedite atomization and vaporization thereof, while during the heavy load operation of the engine, the air-fuel mixture is supplied also through the heavy load side intake passage of the large cross sectional area for improvement of the engine output.
In the conventional air-fuel mixture intake systems, for minimizing undesirable noxious compounds such as unburned hydrocarbon compound in the exhaust gases and also to prevent after-burning, it has been a conventional practive to provide an on-off valve, in a fuel supplying passage of an engine carburetor, for suspension of fuel supply from the fuel supplying passage during engine deceleration by closing the on-off valve. The above known arrangement, however, has such disadvantages that starting of fuel supply tends to be delayed at re-acceleration after engine deceleration, and that undesirable knocking phenomenon is developed at an initial stage of the acceleration, with consequent deterioration in the running performance of a vehicle. For example, in U.S. Pat. No. 3,080,858, supply of fuel is cut off by closing a fuel supplying passage of slow fuel system during deceleration.
Similarly, there have conventionally been proposed another arrangements, for example, in U.S. Pat. No. 3,081,985 in which primary air is introduced during engine deceleration through negative pressure at downstream of a throttle valve in the intake passage. This known arrangement, however, still have some problems to be solved for optimum reduction of hydrocarbon compound formation at the engine deceleration, and for prevention of after-burning and knocking.
Accordingly, an essential object of the present invention is to provide an improved air-fuel mixture intake system for use in an internal combustion engine which fully utilizes advantages of a duplex air-fuel mixture intake system for reducing generation of noxious hydrocarbon compound at deceleration and also for prevention of undesirable after-hurning.
Another important object of the present invention is to provide an air-fuel mixture intake system of the above described type which is free from the knocking phenomenon at an initial stage of acceleration, with substantial elimination of disadvantages inherent in the conventional air-fuel mixture intake systems.
A further object of the present invention is to provide an air fuel mixture intake system of the above described type which is simple in structure and highly reliable, and can be readily incorporated into internal combustion engines of the kind at low cost.
In accomplishing these and other objects, according to one preferred embodiment of the present invention, the air-fuel mixture intake system is intended for use in an internal combustion engine having a light load side intake passage and a heavy load side intake passage which are joined each other in vicinity of intake valve for an intake port of the internal combustion engine, and includes means for detecting deceleration of engine speed, first on-off valve provided in a fuel supplying path of a light load side carburetor, with the first on-off valve being closed, during the engine deceleration, through first actuating means operated by signal from said deceleration detecting means for interrupting supply of fuel through the fuel supplying path, an air supplying passage opened at its one end into the heavy load side intake passage at downstream of a heavy load side carburetor throttle valve, and second on-off valve provided in said air supplying passage, with the second on-off valve means being actuated to be opened, during the engine speed deceleration, through a second actuating means operated by detection of the engine deceleration for supplying air into said heavy load side intake passage through said air supplying passage.
In other words, according to the air-fuel mixture intake system of the present invention, the fuel supply interrupting means is provided in the light load carburetor side to stop the fuel supply at the light load side during the engine deceleration, and the air supply means is provided to supply air in the high load side intake passage during engine deceleration, for reducing formation of the unburned noxious compound, e.g., hydrocarbon and preventing the undesirable after-burning, whereby at the acceleration after the engine deceleration, since the flow rate of the air-fuel mixture flowing through the light load side intake passage of the small cross sectional area is sufficiently fast with favorable atomization, and the air supply during deceleration is not in the light load side intake passage but in the high load side intake passage, delay in starting the fuel supply is prevented, with generation of the knocking being advantageously prevented.